I believe the experiment should go something like this:
- Assume your unknown is the lightest (as is has the lowest grams per moles compared to the others). NaHCO3 has a relative mass of 84 grams per mole, so if your using say 3 grams of the unknown substance you will need at least 3/84 moles of H2SO4 for a complete reaction. I believe you should use a tiny bit more to ensure that you will get a complete reaction regardless of what the unknown is.
- I guess you either do the experiment on a scale or weight the beaker your doing the test in before and after the experiment to determine the mass different and hence the mass of the CO2 given off. once you know the mass of the CO2 you can determine the number of moles of CO2 and therefore the number of moles of the unknown substance you had. you know the mass of the substance you used so you will be able to work out its relative mass and hence determine what it is.